Source:

Response:

Haeckel's pictures are irrelevant to the question of whether the
embryos are similar. What matters are the embryos themselves. Within
a group, early embryos do show many similarities. For example, all
vertebrates develop a notochord, body segments, pharyngeal gill
pouches, and a post-anal tail. These fundamental similarities indicate
a common evolutionary history. Other embryological similarities are
found in other lineages, such as mollusks, arthropods, and annelids.
These similarities have been long known. Professor Agassiz in 1849,
for example, said, "We find, too, that the young bat, or bird, or the
young serpent, in certain periods of their growth, resemble one another
so much that he would defy any one to tell one from the other--or
distinguish between a bat and a snake." (Scientific American 1849)

The embryos also show some differences, which Haeckel glossed over.
However, differences should also be expected, since the animals are not
all equally related. It is the pattern of both similarities and
differences that displays patterns of descent. Organisms that are
less closely related are expected to look less similar.

When Haeckel's inaccuracies were exposed, authors started using
corrected versions. Science tends to be self-correcting.